The present invention relates to the use of electrophoretically deposited patternable material, e.g., photoresist. More particularly, the present invention pertains to the use of electrophoretically deposited patternable material on surfaces with structures thereon such as spacers used in flat panel displays.
Displays take many different configurations. In many displays (e.g., flat panel displays, field emission displays) it is required that photoresist be deposited on surfaces having structures projecting therefrom, e.g., spacers on a face plate surface of a flat panel display. Such structures projecting from the surfaces reduce the effectiveness of conventional photoresist application methods used in the formation of features on the surfaces, e.g., photoresist used for patterning phosphors on face plate surfaces.
For example, as described in U.S. Pat. No. 5,486,126, entitled xe2x80x9cSpacers For Large Area Displays,xe2x80x9d issued Jan. 23, 1996, and assigned to Micron Display Technology, Inc., flat panel displays include a cathode emitting structure and a corresponding anode display structure for use in displaying one or more color images on the display. In such field emission devices, there is a relatively high voltage differential between the cathode emitting structure (also referred to as base electrode, base plate, emitter surface, cathode surface, etc.) and the anode display structure (also referred to as an anode, cathodoluminescent screen, display screen, face plate, or display electrode). As indicated in U.S. Pat. No. 5,486,126, it is important that electrical breakdown between the electron cathode emitting structure, i.e., base plate, and the anode display structure, i.e., face plate, be prevented. At the same time, however, narrow spacing between the base plate and face plate is necessary to maintain a desired structurally thin display and to obtain high image resolution. To provide for such narrow spacing, it is required that various features, e.g., spacers, exist between the base plate and face plate of the display.
Spacers incorporated between the display face plate and base plate have certain characteristics. For example, such spacer structures are generally nonconductive to prevent electrical breakdown between the face plate and base plate in spite of the relatively close spacing therebetween and relatively high voltage differential, e.g., 300 or more volts. However, such spacer structures may have portions that are conductive.
The spacers may include pillars as described in U.S. Pat. No. 5,486,126; support structure as described in U.S. Pat. No. 5,667,418 entitled xe2x80x9cMethod Of Fabricating Flat Panel Device Having Internal Support Structure,xe2x80x9d issued Sep. 16, 1997; spacer structure as described in U.S. Pat. No. 5,675,212 entitled xe2x80x9cSpacer Structure For Use In Flat Panel Displays And Methods For Forming Same,xe2x80x9d issued Oct. 7, 1997; spacers as described in U.S. Pat. No. 5,634,585 entitled xe2x80x9cMethod For Aligning And Assembling Spaced Components,xe2x80x9d issued Jun. 3, 1997; U.S. Pat. No. 5,503,582 entitled xe2x80x9cMethod For Forming Spacers For Display Devices Employing Reduced Pressures,xe2x80x9d issued Apr. 2, 1996; U.S. Pat. No. 5,232,549 entitled xe2x80x9cSpacers For Field Emission Display Fabricated Via Self-Aligned High Energy Ablation,xe2x80x9d issued Aug. 3, 1993; and U.S. Pat. No. 5,205,770 entitled xe2x80x9cMethod To Form High Aspect Ratio Supports (Spacers) For Field Emission Display Using Micro-saw Technology,xe2x80x9d issued Apr. 27, 1993; or any other spacer configuration, such as a screen printed feature, a stencil printed feature, glass spheres, etc.
Such spacers are fixed in one manner or another to either the face plate or the base plate. In many circumstances, such as when processes involved in making the base plate prevent the adhesion of spacers thereto or when such processes may weaken or damage the spacers, it is required that such spacers be attached or otherwise affixed to the face plate. Further, when the light emitting material, e.g., phosphors, impedes the adhesion of the spacers to the face plate, the spacers must be attached to the face plate prior to the phosphors being formed thereon. For example, U.S. Pat. No. 5,486,126 describes a method of disposing micropillar spacers on a surface of the face plate of a display.
Phosphors deposited on the surface of the face plate emit energy when excited by electrons. Phosphors are normally composed of inorganic luminescent materials that absorb incident radiation and subsequently emit radiation within the visible region of the spectrum. Phosphors are preferably capable of maintaining luminescence (e.g., fluorescence) under excitation for a relatively long period of time to provide superior image reproduction. Various phosphors include, for example, Y2O3:Eu, ZnS:Ag, Zn2SiO4:Mn, ZnO:Zn, or other doped rare earth metal oxides.
Affixation of the spacers to the face plate structure of a display prior to deposition of phosphors thereon presents problems in the deposition and patterning of such phosphors. Such problems result at least in part from the lack of ability to provide a uniform layer of patternable material in the regions between the spacers and, in particular, in areas directly adjacent to the spacers. A uniform layer of patternable material is necessary so that photolithographic processes can be effectively performed, as is done using phosphor slurries to make CRT screens, e.g., as described in U.S. Pat. No. 3,387,975 entitled xe2x80x9cMethod Of Making Color Screen Of A Cathode Ray Tube,xe2x80x9d issued Mar. 10, 1965.
For example, if the face plate having the spacers projecting therefrom is coated with a patternable material, e.g., resist, by spin coating, areas of noncoating or minimal coating may occur on the face plate adjacent the spacers as a result of such spacers blocking the flow of the patternable material. The patternable material also tends to form a meniscus with the spacers, resulting in a layer that is generally too thick and very non-uniform, particularly in regions adjacent to the spacers. Similar problems occur with meniscus, dip, or spray coating techniques.
Electrophoretic photoresist technology has been described in various articles and patents. For example, the article by D.A. Vidusek, entitled xe2x80x9cElectrophoretic Photoresist Technology: An Image of the Futurexe2x80x94Today,xe2x80x9d presented in December 1988 at the EIPC Winter Conference in Zurich, Switzerland, describes electrophoresis as a new technique for applying photoresist. Further, such electrophoretic deposition processes and photoresist for use in such processes are described in U.S. Pat. No. 4,592,816, entitled xe2x80x9cElectrophoretic Deposition Process,xe2x80x9d issued Jun. 3, 1986; U.S. Pat. No. 4,751,172, entitled xe2x80x9cProcess For Forming Metal Images,xe2x80x9d issued Jun. 14, 1988; U.S. Pat. No. 5,004,672, entitled xe2x80x9cElectrophoretic Method for Applying Photoresist to Three-Dimensional Circuit Board Substrate,xe2x80x9d issued Apr. 2, 1991; U.S. Pat. No. 5,196,098, entitled xe2x80x9cApparatus and Process for Electrophoretic Deposition,xe2x80x9d issued Mar. 23, 1993; and U.S. Pat. No. 5,607,818 entitled xe2x80x9cMethod For Making Interconnects And Semiconductor Structures Using Electrophoretic Photoresist Deposition,xe2x80x9d issued Mar. 4, 1997.
To overcome the problems described above, and others which will be apparent from the detailed description below, a patternable material is electrophoretically deposited to give uniform resist thicknesses on surfaces having features, e.g., spacers, projecting therefrom, such as are common to many flat panel display face plates. The electrophoretically deposited patternable material may then be used for forming various structures such as light emitting elements relative to the face plate, e.g., color patterning for a color display.
A method for use in the production of a face plate of a display according to the present invention includes providing a substrate assembly of the display face plate with the substrate assembly including a conductive surface at a first side of the assembly. One or more projections extend from the first side of the substrate assembly. A patternable material, e.g., electrophoretically depositable resist, is electrophoretically deposited on the conductive surface and adjacent the projections.
In various embodiments of the method, the one or more projections include a plurality of spacers extending from the first side of the substrate assembly. The spacers may be nonconductive or have at least portions thereof that are slightly conductive.
In another embodiment of the method, patterning of the patternable material results in a first patterned layer defining openings to the conductive surface for use in deposition of one or more light emitting elements on the conductive surface. Further, the method may include forming one or more first color light emitting elements on the conductive surface through the defined openings in the first patterned layer. The first patterned layer is then removed after the one or more first color light emitting elements are formed resulting in exposed regions of the conductive surface. Yet further, the electrophoretic deposition and patterning of patternable material and the forming of light emitting elements on the conductive surface may be repeated to form additional light emitting elements of one or more additional colors on the conductive surface.
In yet another embodiment of the method, the electrophoretic deposition of the patternable material over the conductive surface and adjacent the projections may include electrophoretically depositing a patternable material mixed with a light emitting material over the conductive surface and adjacent the projections.
In yet further another embodiment, the method may include patterning the patternable material by tackifying one or more surface regions of the deposited patternable material for use in depositing the light emitting material.
Another method for use in the production of a display according to the present invention includes providing a substrate assembly including a conductive surface and providing one or more nonconductive regions formed on the conductive surface. The one or more nonconductive regions have a thickness less than about 15 microns. A layer of patternable material is formed by electrophoresis over the conductive surface and the one or more nonconductive regions.
In various embodiments of the method, the one or more nonconductive regions may include one or more nonconductive light emitting elements, e.g., phosphors and/or the one or more nonconductive regions may include a nonconductive black matrix. Further, the method may include patterning the patternable material resulting in a patterned layer defining openings to the conductive surface for use in formation of light emitting elements on the conductive surface.
A method for use in producing a display having a face plate and a base plate according to the present invention is also described. The face plate has one or more spacers extending from one side thereof for spacing the face plate from the base plate in the display. The method includes electrophoretically depositing a patternable material over a conductive surface of the face plate in regions adjacent one or more of the spacers, patterning the patternable material resulting in a patterned layer defining a openings to the conductive surface, and forming a material on the conductive surface through the defined openings. The patterned layer is then removed.
Yet another method according to the present invention is described for use in the production of a color display to deposit a pattern of light emitting elements capable of emitting light of at least two different colors when excited. The display includes a face plate having a plurality of spacers extending from one side thereof for use in spacing the face plate from a base plate of the color display. The method includes providing a face plate substrate assembly from which the spacers extend. A conductive surface is exposed in regions between the plurality of spacers. An electrophoretically deposited patternable material is used to form the pattern of light emitting elements on the conductive surface. The light emitting elements may be formed in a number of ways. For example, the elements may be formed using electrophoretic deposition of a light emitting material after patterning an electrophoretically deposited patternable layer or may be formed by patterning a deposited layer of a mixture of patternable material and light emitting material. Further, the light emitting elements may be formed by tackification of the patternable layer followed by dusting with the light emitting material.